=29. Estimation of Lime.=—One hundred cubic centimeters of the solution (containing one gram of the original substance) are evaporated in a beaker to about fifty cubic centimeters; ten cubic centimeters of dilute sulfuric acid (one to five) are added; and the evaporation is continued on the water-bath until a considerable crop of crystals of gypsum has formed[20]. The solution is then allowed to cool, when it generally becomes pasty, owing to the separation of additional gypsum. When it is cold, 150 cubic centimeters of ninety-five per cent alcohol are slowly added, with continual stirring, and the whole is allowed to stand for three hours, being stirred from time to time. After three hours, it is filtered, with the aid of a filter-pump, into a distillation flask, and the beautifully crystalline precipitate, which does not adhere to the beaker, is washed with ninety-five per cent alcohol. The filter, with the precipitate, is gently removed from the funnel and inverted into a platinum crucible, so that, by squeezing the point of the filter, the precipitate is made to fall into the crucible, and the paper can be pressed down smoothly upon it. On gentle heating of the crucible, the remaining alcohol burns off, and when the paper has been completely destroyed, the heat is raised to the full power of a bunsen for about five minutes. After cooling in a desiccator the crucible containing the calcium sulfate, is weighed. The filtration may also be accomplished on asbestos felt. =30. The Ammonium Oxalate Method.=—This method has been extensively used in this country in commercial work, and is best carried out as described by Wyatt.[21] The total filtrates from the iron and alumina precipitates, secured as described in paragraph =33=, are well mixed and concentrated to a volume of about 100 cubic centimeters. There are added about twenty cubic centimeters of a saturated solution of ammonium oxalate, and after stirring, the mixture is allowed to cool and remain at rest for six hours. The supernatant liquid is poured through a filter, the residue washed three times by decantation with hot water and brought upon the filter. The beaker and precipitate are washed at least three times. The precipitate is dried and ignited at low redness for ten minutes. The temperature is then raised by a blast and the ignition continued for five minutes longer, or until the lime is obtained as oxid. The precipitate is likely to contain magnesia. The magnesia is estimated in the filtrates from the lime determination by first mixing them and concentrating to 100 cubic centimeters, which, after cooling, are made strongly alkaline with ammonia. After allowing to stand for twelve hours the ammonium magnesium phosphate is collected and reduced to magnesium pyrophosphate by the usual processes. If one gram of the original material has been used the pyrophosphate obtained, multiplied by 0.36, will give the weight of magnesia contained therein.